Algorithmic Responding on the Radial Maze in Rats does not Always Imply Absence of Spatial Encoding

Sources of variation in search and foraging: A theoretical perspective

Search-the problem of exploring a space of alternatives to identify target goals-is a fundamental behaviour for many species. Although its foundation lies in foraging, most studies of human search behaviour have been directed towards understanding the attentional mechanisms that underlie the efficient visual exploration of two-dimensional (2D) scenes. With this review, we aim to characterise how search behaviour can be explained across a wide range of contexts, environments, spatial scales, and populations, both typical and atypical. We first consider the generality of search processes across psychological domains. We then review studies of interspecies differences in search. Finally, we explore in detail the individual and contextual variables that affect visual search and related behaviours in established experimental psychology paradigms. Despite the heterogeneity of the findings discussed, we identify that variations in control processes, along with the ability to regulate behaviour as a function of the structure of search space and the sampling processes adopted, to be central to explanations of variations in search behaviour. We propose a tentative theoretical model aimed at integrating these notions and close by exploring questions that remain unaddressed.

Gender, videogames and navigation in virtual space

Spatial abilities associated with success in educational and occupational fields of Science, Technology, Engineering, and Mathematics (STEM) have been repeatedly shown to be gendered, with males demonstrating measurably better spatial abilities than females. Less is known about why this is, or about how experience with spatial systems (videogames, for example) affects these abilities. We conducted two experiments with 82 participants with varying degrees of videogame experience on measures of mental rotation, spatial learning, and spatial memory. Spatial learning and memory were tested in a Virtual Morris Water Maze. In the first experiment, the maze lacked proximal landmarks. Males proved faster and more accurate than females in learning the location of the hidden platform. As predicted males also outperformed females in mental rotation abilities. Mental rotation correlated with performance in the virtual maze, indicating that in the absence of proximal landmarks, participants relied on strategies requiring mental rotation. Experienced 3D videogame players did not demonstrate superior spatial learning and memory, but performed better than novices in mental rotation. In the second experiment, the maze had proximal cues, in the form of landmarks on the circumference of the virtual pool, and gender-based differences in navigational performance significantly diminished. Under these changed environmental conditions, mental rotation ability did not correlate with performance in the VMWM, suggesting that given proximal cues, the need for mental rotation diminishes. Differences between videogame novices and experts also decreased when proximal cues were provided. Females in particular obtained more discernible benefits from videogame experience. Together, these experiments reveal how the spatial abilities and strategies used to solve the Morris maze task vary with environmental design. Given the structural similarities between the virtual maze and videogame environments, these results offer insight into how spatial experience gained through videogame playing can affect aspects of spatial cognition, and can help identify design elements that contribute to their improvement.

Reorganization of cues and path organisation in dogs

Dogs were submitted to a free search for food which was distributed in six feeding points situated on a circle. In the first part of the experiment they were able to reorganize information collected on radial paths leading from the center to the feeding points in order to invent new routes between these points. There were considerable differences in the degree of stereotypy and variability of visit sequences between the six dogs used in this experiment, with overtraining tending to induce locomotory habits in dogs using varied sequences. These habits were not however disconnected from the representational processes, since dogs used a variety of sequences without making any error when the starting conditions were made to vary. In the second part of the experiment, our aim was to analyse whether, without taking environmental cues into account, the dogs were able to learn that stable geometrical relationships existed among three food-points and between these points and the starting place. The dogs' behavior showed that they were able to learn something about the experimental rule. However it is not clear if they have detected the geometrical relationships among baited food-points, or the simultaneous presence of food at specific points, or both.

Relationships between the superior colliculus and hippocampus: Neural and behavioral considerations

Theories of superior collicular and hippocampal function have remarkable similarities. Both structures have been repeatedly implicated in spatial and attentional behaviour and in inhibitory control of locomotion. Moreover, they share certain electrophysiological properties in their single unit responses and in the synchronous appearance and disappearance of slow wave activity. Both are phylogenetically old and the colliculus projects strongly to brainstem nuclei instrumental in the generation of theta rhythm in the hippocampal EEC

On the other hand, close inspection of behavioural and electrophysiological data reveals disparities. In particular, hippocampal processing mainly concerns stimulus ambiguity, contextual significance, and spatial relations or other subtle, higher order characteristics. This requires the use of largely preprocessed sensory information and mediation of poststimulus investigation. Although collicular activity must also be integrated with that of “higher” centres (probably to a varying degree, depending on the nature of stimuli being processed and the task requirements), its primary role in attention is more “peripheral” and specific in controlling orienting/localisation via eye and body movements toward egocentrically labelled spatial positions. In addition, the colliculus may exert a nonspecific influence in alerting higher centres to the imminence of information potentially worthy of focal attention. Nevertheless, it is noteworthy that collicular and hippocampal lesions produce deficits on similar tasks, although the type of deficit is usually different (often opposite) in each case. Functional overlap between hippocampus and colliculus (i.e., strategically synchronised or mutually interdependent activity) is virtually certain vis-à-vis stimulus sampling, for example in the acquisition of information via vibrissal movements and visual scanning. In addition, insofar as stimulus significance is a factor in collicular orienting mechanisms, the hippocampus — cingulate – cortex — colliculus pathway may play a significant role, modulating collicular responsiveness and thus ensuring an attentional strategy appropriate to current requirements (stimulus familiarity, stage of learning). A tentative “reciprocal loop” model is proposed which bridges physiological and behavioural levels of analysis and which would account for the observed degree and nature of functional overlap between the superior colliculus and hippocampus.

Spatial pattern learning in the radial arm maze

Rats experienced a spatial pattern of baited and unbaited arms in an eight-arm radial maze. The spatial pattern remained constant over trials, but the spatial locations that were baited varied unpredictably. Although there was no evidence of control by the spatial pattern during free choice training trials, the rats' ability to locate baited arms in forced choice test trials was superior to that of animals in a control condition for which maze arms were not baited in a consistent spatial pattern. This is consistent with the results of experiments showing that spatial choices by rats in a pole box maze are controlled by abstract spatial patterns.

Learning to cope with two different food distributions: the performance of house mice (Mus musculus domesticus)

Search abilities of mice (Mus musculus domesticus) were evaluated using an arena closed by a ceiling in which 9 food sources (which mice could reach standing on their hind legs) could be arranged according to 2 configurations: a 3 x 3 square matrix and 3 clusters each containing 3 food sources. Testing conditions prevented olfactory and visual cues from being left after visits to food sources, and mice were able to choose alternative routes between food sources. Results showed that mice were more efficient with the matrix than with the cluster configuration. Sex differences were observed: Females improved their performance with both configurations, whereas males improved only with the matrix one. Mice did not develop evident search strategies that would minimize task complexity. Comparison with data published on capuchin monkeys revealed differences, with monkeys performing better with the cluster configuration than with the matrix and applying searching strategies.

Individual differences in radial maze performance and locomotor activity in the meadow vole, Microtus pennsylvanicus

Individual differences in the radial maze performance and locomotor activity of wild-caught and first-generation laboratory-born meadow voles are described. Based on their patterns of response in an eight-arm radial maze the essentially wild voles fell into three behavioral categories: 1) strict algorithmic (i.e., they systematically chose the next adjacent arm to their previous choice); 2) nonalgorithmic (i.e., they ran the maze without any consistent or definable pattern); and 3) nonrunners (i.e., nonperformers of the task who remained relatively immobile in the arms of the maze). The algorithmic and nonalgorithmic voles further differed in their responses to an interference manipulation of the radial maze task. Algorithmic individuals displayed a marked performance deficit, while the nonalgorithmic individuals showed minimal disruption to a 1-min delay interruption of the maze task. Measurements of several aspects of locomotor activity using the automated Digiscan activity monitoring system revealed that the algorithmic individuals also displayed significantly greater levels of activity than the nonalgorithmic or nonrunners, with no significant difference in activity between the latter two groups. These findings suggest that the algorithmic voles were relatively inflexible in their behavior, while the nonalgorithmic individuals were more flexible in their maze performance and likely in their use of spatial and nonspatial information. These individual differences in laboratory measures of learning behavior and locomotor activity in meadow voles are consistent with the polymorphism that is proposed to occur in the wild.

The role of inferior parietal cortex and fornix in route following and topographic orientation in cynomolgus monkeys

The effects of inferior parietal cortex lesions (Area 7a/PG) and bilateral transection of the fornix were compared within a single species (cynomolgus monkeys) and using a single paradigm of route running in a traditional (fixed entry and exit) whole-body maze. Experiment 1 showed that Area 7a/PG but not fornix lesions impaired post-operative retention of route running. Experiment 2 assessed the contribution of visual cues and proprioceptive/kinaesthetic guidance to route running and showed that in non-lesioned monkeys route running was influenced to varying degrees by proprioceptive guidance, visual extra-maze room cues and visual maze stimuli. Post-operative assessment of maze performance, including error patterns, retraining and misreaching (Experiment 1), suggested that monkeys in the Parietal Group were not topographically disoriented and did not have a spatial long-term memory deficit, but it was their difficulty responding to local spatial cues which initially impaired route running. Investigation of cue use (Experiment 2) also showed the sensitivity of the Parietal Group to local spatial cues; they were significantly impaired on entry through a new start position when the relationship between maze stimuli and extra-maze cues was changed. The Fornix Group showed no retrograde long-term memory deficit for route-running (Experiment 1). However, in Experiment 2, where a new goal position was learnt, the Fornix Group did show an anterograde memory deficit.

Ontogeny of orientation and spatial learning on the radial maze in mice

The development of the orientation capacities of C57BL/6 mice has been studied on the radial maze in several procedures allowed to dissociate the different types of cues used by the mouse for solving the task with two intersession delays (2 and 24 hr). The results of the first two studies show that performance is independent of intersession delay regardless of the age of the subject. Mice as early as 23 days old obtain good performances when they can develop an algorithmic strategy or when they dispose of both proximal and distal cues during learning. At 37 days of age, however, mice can efficiently solve the radial maze task with distal cues alone. However, in the third experiment, 23-day-old mice were able to use distal cues for orientation at the end of the learning session if, at the onset, they also had access to proximal cues. These results suggest that, on weaning, mice use several types of information for task performance and that, as they mature, they turn more often to distal cues for orientation.

Drug effects in a radial maze designed for dissociation of cues used by mice

Scopolamine and amphetamine effects were investigated in a new radial maze. Three distinct procedures were designed to dissociate the use, by C57BL/6 mice, of the different cues available: a procedure where only spatial information was available, a procedure in which both spatial cues and olfactory trials were present, and a nonconfinement procedure where mice could use spatial cues, olfactory trials, and/or algorithmic strategies. We found that while scopolamine impaired performance on the maze in all three procedures, amphetamine tended to improve solving of the maze problem, but only in the procedure where spatial cues alone were available. The results are discussed in relation to hypotheses concerning these drug effects.

Functional consequences of a single nerve growth factor administration following septal damage in rats

This study examined how possible nerve growth factor (NGF)-induced behaviour changes after septal damage might be modulated by the lesion extent, the dose of NGF administered and the delay between surgery and the onset of testing. In a first experiment, young rats which received electrolytic septal lesions of high or low intensity (inducing respectively large and mild lesions) were treated with 10 or 30 micrograms NGF administered intrahippocampally in a single injection. They were tested 4 months postoperatively for open field ambulation, spontaneous alternation and radial maze performance. It was observed that irrespective of the severity of the lesions rats were impaired in the spontaneous alternation and radial maze tests; however, no obvious changes appeared in the open field test. While an NGF injection did not affect behavioural performances in rats with large lesions, it was capable of ameliorating behavioural deficits in the spontaneous alternation and radial maze tests of rats with mild lesions in both NGF dosage groups. It was also seen that lesions produced a general decrease in hippocampal choline acetyltransferase (ChAT) activity, which was not significantly affected by an NGF administration. There was no significant correlation between ChAT activity and behavioural performance of NGF-treated rats. In a second experiment, young rats received mild septal lesions and were treated with 10 micrograms NGF. These rats were tested 2 weeks postoperatively for radial maze performance. NGF rats exhibited similar behaviour to controls with regard to all of the variables measured. The present results suggest that a single NGF administration spares some abilities to use spatial information efficiently providing lesions are partial.

A study of behavioral and sensorial bases of radial maze learning in mice

In order to analyze the various sensorial and behavioral modes implied in learning on a radial maze, three isogenic mice groups (BALB/C, C57BL/6, and CB6F1) were subjected to four different learning procedures, each ending with a probe test. These four procedures examined the use of radial strategies and allowed to dissociate the use of olfactory and spatial cues. Results showed that all mice preferred to use a radial strategy. When the confinement procedure rendered the use of a radial strategy impossible, BALB/C mice were incapable of establishing spatial orientation but were able to learn the task by using olfactory cues. C57BL/6 mice, on the other hand, seemed to use spatial cues exclusively, while the CB6F1 hybrids showed a high degree of plasticity, using either type of information. These strain-specific differences point out the heterogeneity of the processes called into play during radial maze learning and show that unless olfactory cues are carefully controlled they can account for choice accuracy in some mice.

Can rats solve a simple version of the traveling salesman problem?

Whereas correct tours through the radial arm maze are almost equally long, free choice mazes with multiple goals scattered in an open field allow the animal to select the shortest one from a multitude of correct tours. Thirteen rats were trained (at 10 trials per day) to visit an array of cylindrical feeders in an open field (40 x 100 cm) with reward available only when visiting the last feeder of the set. In Expt. 1 with eight feeders arranged in five different configurations the rats made after 10 days of training 1 error in the first 8 choices and incidence of errorless trials was about 20%. In Expt. 2. the use of six feeders in a rectangular (A) or double triangle (B) configuration increased the incidence of errorless trials to 60%. Expt. 3 showed that performance in the 6-feeder maze was significantly impaired by 6 mg/kg ketamine or 0.25 mg/kg scopolamine but not by lower dosages of these drugs. Tours generated on errorless trials (each feeder visited only once) during 10 days of Expt. 2 were analyzed. Six places can be visited in 6! = 720 different closed tours the lengths of which (in arbitrary units) range from 6.00 to 10.12 for A and from 6.83 to 10.47 for B. Whereas random generation of correct routes yielded only 5% of the shortest tours, they were clearly preferred by rats (41% in A and 45% in B). The apparent proficiency of rats in this optimization problem is probably not due to cognitive comparison of the possible correct routes but rather to following a simple rule 'Always go to the nearest not yet visited feeder'.

Locomotion, active choice, and spatial memory in children

In two studies, children between 4 and 6 years old were tested on a radial search task requiring nonredundant sampling of eight identically labeled positions in a room. In the training phase (5 days), children made free choices by walking between positions, were passively transported in a pushchair, actively directed their own route from a pushchair, or were led on foot to positions selected by the experimenter. When tested (whether walking or directing while seated in a pushchair), children who had either walked independently or directed the experimenter while being pushed performed competently; those led on foot without spatial choice performed almost as well. Only the children who had neither independent locomotor experience nor autonomous choice performed very poorly. The results are related to neurobiological models of spatial cognition and may have implications for the transportation of children with mobility problems.

Early rearing environment and dorsal hippocampal ibotenic acid lesions: long-term influences on spatial learning and alternation in the rat

Behavioural responses in a set of spatial and cue tasks were assessed in adult rats that had been given ibotenic acid lesions of the dorsal hippocampus at weaning. The lesions or sham operations were immediately followed by one month of differential rearing, either in enriched, social or isolated housing environments. The differential rearing was followed by standard (social) housing conditions until behavioural testing began at 4 months of age. Compared to sham-operated rats, the rats with early cytotoxic lesions showed substantial impairments on learning and efficient strategy formation in radial arm maze, retention of a spatial location, but not of a cue-marked location, in a + maze and spontaneous alternation. Differential rearing had some long-term effects depending on the task. Sham-operated rats which had been housed in isolation used a pattern of strategies in the radial arm maze that resembled the pattern used by rats with lesions. Early enrichment, on the other hand, alleviated lesion deficits only in a spontaneous alternation task in a T-maze where the variety and salience of proximal cues were maximised. Enrichment increased lesion deficits in the radial maze task, where distal cues only could guide performance. The results suggest that the hippocampus may play an important role in the use of contextual information and that behavioural recovery after early hippocampal damage--limited to situations in which featural information is highly salient--may be permanently induced by rearing in environments, as in enriched ones, where rats can attend to and manipulate environmental cues.